Epoxy resin composition and semiconductor apparatus

ABSTRACT

The object of the present invention is to provide an epoxy resin composition which is excellent in flash characteristics and thermal conductivity, and gives an area mounting type semiconductor apparatus having little warpage and excellent temperature cycle properties. According to the present invention, there is provided an epoxy resin composition for semiconductor encapsulation which comprises, as essential components, (A) a spherical alumina, (B) an ultrafine silica having a specific surface area of 120-280 m 2 /g, (C) a silicone compound, (D) an epoxy resin, (E) a phenolic resin as a curing agent, and (F) a curing accelerator, in which said ultrafine silica is contained in an amount of 0.2-0.8% by weight based on the total weight of the resin composition, and said silicone compound is a polyorganosiloxane and is contained in an amount of 0.3-2.0% by weight based on the total weight of the resin composition.

BACKGROUND OF THE INVENTION

The present invention relates to an epoxy resin composition forencapsulation of semiconductors and a semiconductor apparatus.

In accordance with the recent trend of market for miniaturization,weight-saving and high performance of electronic devices, highintegration of semiconductors has advanced year by year, and,furthermore, surface mounting of semiconductor apparatus has beenpromoted. Under the circumstances, area mounting type semiconductorapparatuses have been newly developed and shifting to such newsemiconductor apparatuses from those of conventional structures hasstarted.

As area mounting type semiconductor apparatuses, representative are ballgrid array (hereinafter referred to as “BGA”), and further miniaturizedchip size package (hereinafter referred to as “CSP”), and these havebeen developed for meeting the demand for increase of the number of pinsand speeding-up which have reached the limits with the surface mountingtype semiconductor devices such as quad flat package (hereinafterreferred to as “QFP”) and small outline package (hereinafter referred toas “SOP”).

As for the structures of the area mounting type semiconductor devices,semiconductor elements are mounted on one side of a rigid circuitsubstrate such as a bismaleimide triazine (hereinafter referred to as“BT”) resin/copper foil circuit substrate or a flexible circuitsubstrate such as polyimide resin film/copper foil circuit substrate,and only the side of the substrate on which elements are mounted,namely, only the one side of the substrate is encapsulated with a resincomposition by molding. Furthermore, on the side of the substrateopposite to the side on which the semiconductor elements are mounted,solder balls are two-dimensionally aligned and bond the substrate to acircuit substrate on which semiconductor devices are mounted. Moreover,as a substrate on which elements are mounted, there is proposed astructure which uses a metal substrate such as a lead frame in additionto the above organic circuit substrates.

These area mounting type semiconductor apparatuses have a structure ofone-side encapsulation type according to which only the side of asubstrate on which elements are mounted is encapsulated with a resincomposition and the side on which solder balls are provided is notencapsulated. Very rarely, in the case of a metal substrate such as alead frame, an encapsulation resin layer of several ten μm may also bepresent on the side on which solder balls are present, but anencapsulation resin layer of several hundred μm to several mm is formedon the side on which elements are mounted, and, therefore, this issubstantially a one-side encapsulation type. Accordingly, warpages areapt to occur in these semiconductor apparatuses just after molding owingto mismatching in thermal expansion or thermal shrinkage between theorganic substrate or metal substrate and the cured resin composition orowing to influence of curing shrinkage during molding and curing of theresin composition.

On the other hand, generation of heat from the semiconductor devicesteadily increases, and the necessity to dissipate the heat generatedfrom the semiconductor device to the outside of the package through theepoxy resin composition for encapsulation of semiconductors has recentlybecome very important. Hitherto, in the structure of area mounting typesemiconductor apparatus, increase of the number of pins of externalterminals and miniaturization of package are easy because of possibilityof area mounting, and, hence, application of semiconductor devices whichgenerate a large quantity of heat is promoted, and notice is given todissipation of heat to the outside of the package (PKG). Particularly,in order to promote heat dissipation from the epoxy resin composition tothe outside, metal plates which are high in heat dissipation areattached to the package, but there is the limit in promotion of the heatdissipation unless the heat dissipation of the epoxy resin compositionfor semiconductor encapsulation per se is promoted, and importance ofpromotion of heat dissipation of the epoxy resin composition isparticularly noticed.

However, hitherto, epoxy resins for encapsulation high in thermalconductivity have been developed utilizing alumina and the like(JP-B-7-47682, pages 1-6 and Japanese Patent No. 2874089, pages 1-8),but when they are applied to structures of area mounting typesemiconductor apparatuses, there are problems in moldability,especially, bad flash characteristics and leakage of flashes onto thesubstrate. Furthermore, because of the high modulus of elasticity,warpage occurs in the package and temperature cycle properties areinferior, and hence development of new epoxy resins for encapsulationhaving high thermal conductivity is of urgent necessity for areamounting type semiconductors.

The present invention provides an epoxy resin composition forsemiconductor encapsulation in area mounting type semiconductorapparatuses which is excellent in its molding operability, especially,satisfactory in flash characteristics, and furthermore showssubstantially no warpage during soldering treatment after molding andhas high resistance to temperature cycle, high soldering crackresistance and high thermal conductivity, and further provides asemiconductor apparatus obtained using the above epoxy resincomposition.

SUMMARY OF THE INVENTION

According to the present invention, it has been found that an epoxyresin composition for semiconductor encapsulation which has excellentmoldability, low molding shrinkage, high resistance to temperaturecycle, high soldering crack resistance and high thermal conductivity canbe obtained by using a spherical alumina and a specific ultrafine silicaat a specific ratio and further a silicone compound. That is, thepresent invention relates to an epoxy resin composition forsemiconductor encapsulation which comprises, as essential components,(A) a spherical alumina, (B) an ultrafine silica having a specificsurface area of 120-280 m²/g, (C) a silicone compound, (D) an epoxyresin, (E) a phenolic resin curing agent, and (F) a curing accelerator,said ultrafine silica being contained in an amount of 0.2-0.8% by weightbased on the total weight of the resin composition, said siliconecompound being preferably a polyorganosiloxane, and being contained inan amount of preferably 0.3-2.0% by weight based on the total weight ofthe resin composition, and further relates to an area mounting typesemiconductor apparatus produced using the above epoxy resincomposition.

DETAILED DESCRIPTION OF THE INVENTION

The spherical alumina used in the present invention is not particularlylimited as far as it is spherical. The shape of the spherical alumina ispreferably close to true sphere for improvement of flowability. Theaverage particle diameter is preferably 5-30 μm. If the average particlediameter is smaller than the lower limit or exceeds the upper limit, theflowability may be deteriorated. The amount of the spherical aluminaused in the present invention is preferably 85-92% by weight based onthe total weight of the resin composition. If the amount is less thanthe lower limit, thermal conductivity lowers, and besides the moldedproduct of the area mounting type semiconductor apparatus is warped,which is not preferred. If the amount exceeds the upper limit, thermalconductivity is improved, but flowability is inferior, which is notpreferred. Furthermore, if necessary, the spherical alumina used in thepresent invention may be previously coated with a coupling agent, anepoxy resin or a phenolic resin. The coating can be carried out bymixing them using a solvent and thereafter removing the solvent or bydirectly adding them to an inorganic filler and mixing them using amixer.

The ultrafine silica used in the present invention is required to have aspecific surface area of 120-280 m²/g and to be added in an amount of0.2-0.8% by weight based on the total weight of the resin composition.When only the spherical alumina is used, flash characteristics duringmolding are inferior to cause the problem of leakage of the flash ontothe substrate in molding of the area mounting type semiconductorapparatus, but when the ultrafine silica is added, the flashcharacteristics can be considerably improved. The specific surface areaof the ultrafine silica is 120-280 m²/g, and if it is less than thelower limit, long flashes are produced to deteriorate the flashcharacteristics, and if it exceeds the upper limit, the compositionincreases in viscosity to deteriorate flowability. Furthermore, theamount of the ultrafine silica in the whole resin composition is0.2-0.8% by weight, and if the amount is less than the lower limit, longflashes are produced to deteriorate the flash characteristics, and if itexceeds the upper limit, the composition increases in viscosity todeteriorate flowability.

The silicone compound used in the present invention includes siliconerubber, silicone oil, or the like, and a polyorganosiloxane which is asilicone oil is particularly suitable. The polyorganosiloxanes includepolysiloxanes having a skeleton of dimethylpolysiloxane,diphenylpolysiloxane or methylphenylpolysiloxane, and preferably have intheir main chain or side chain an organic substituent having C, O, N orS atom in addition to methyl group or phenyl group in order to impartaffinity with epoxy resins and phenolic resins. Specifically, theorganic substituents include amino group-substituted organic groups,epoxy group-substituted organic groups, hydroxyl group-substitutedorganic groups, vinyl group-substituted organic groups, mercaptogroup-substituted organic groups, carboxyl group-substituted organicgroups, phenethyl group-substituted organic groups, acrylgroup-substituted organic groups, alkoxy group-substituted organicgroups, polyether group-substituted organic groups, caprolactonegroup-substituted organic groups, ureide group-substituted organicgroups, isocyanate group-substituted organic groups, etc., and theorganic substituents are not limited to these examples. When high heatconductive fillers such as alumina are used, the modulus of elasticityof the composition increases, resulting in large warpage duringsoldering treatment after molding, and furthermore the resistance totemperature cycle lowers. The polyorganosiloxane used in the presentinvention has the action to reduce the warpage of semiconductorapparatus caused by decrease in modulus of elasticity of the epoxy resincomposition, and is suitable for relaxation of stress generated at thetime of temperature cycle test and can improve reliability in mounting.The amount of the polyorganosiloxane is preferably 0.3-2.0% by weightbased on the total weight of the epoxy resin composition. If the amountis less than the lower limit, the modulus of elasticity cannot begreatly reduced and the effect to reduce warpage becomes smaller, andtemperature cycle resistance is also inferior, and if it exceeds theupper limit, flowability and curability are deteriorated.

The epoxy resins used in the present invention are all of monomers,oligomers and polymers having epoxy group, and molecular weight andmolecular structure thereof are not particularly limited. Examples ofthe epoxy resins are triphenolmethane type epoxy resins, bisphenol typeepoxy resins, stilbene type epoxy resins, o-cresol novolak type epoxyresins, epoxy resins containing naphthalene skeleton, dicyclopentadienetype epoxy resins, etc. These may be used each alone or in admixture.

The phenolic resins used in the present invention include all ofmonomers, oligomers and polymers having at least two phenolic hydroxylgroups which can form a crosslinked structure through a curing reactionwith the above epoxy resin, and molecular weight and molecular structurethereof are not particularly limited. Examples of the phenolic resinsare phenolic aralkyl resins such as phenolic novolak resins, cresolnovolak resins, p-xylylene-modified phenolic resins andm-xylylene-p-xylylene-modified phenolic resins, resins containingnaphthalene skeleton, terpene-modified phenolic resins,dicyclopentadiene-modified phenolic resins, etc. These may be used eachalone or in admixture.

The curing accelerators used in the present invention include thosewhich can act as catalysts for the crosslinking reaction of the aboveepoxy resin and phenolic resin, and those which are generally used asencapsulating materials can be used. Examples of the curing acceleratorsare amine compounds such as 1,8-diazabicyclo(5,4,0)undecene-7 andtributylamine, organic phosphorus compounds such as triphenylphosphineand tetraphenylphosphonium•tetraphenyl borate, and imidazole compoundssuch as 2-methylimidazole. The curing accelerators are not limited tothese examples. These may be used each alone or in admixture.

The epoxy resin composition of the present invention may optionallycontain, in addition to the components (A)-(F), various additives, forexample, inorganic ion exchangers such as hydrated bismuth oxide andmagnesium-aluminum compounds, coupling agents such asγ-glycidoxypropyltrimethoxysilane, coloring agents such as carbon blackand red oxide, releasing agents such as natural waxes, synthetic waxes,higher fatty acids and metal salts thereof and paraffin, flameretardants such as brominated epoxy resins, antimony oxide, phosphateesters, phosphazene compounds, aluminum hydroxide and magnesiumhydroxide, antioxidants, etc.

The epoxy resin composition of the present invention is obtained by coldmixing the components (A)-(F) and other additives by a mixer, meltkneading the mixture by a kneading machine such as a roll, a kneader oran extruder, cooling the kneaded product and then grinding the product.

In order to make semiconductor apparatuses by encapsulating electronicparts such as semiconductor elements using the resin composition of thepresent invention, cure molding can be carried out by a molding methodsuch as transfer molding, compression molding or injection molding.

DESCRIPTION OF PREFERRED EMBODIMENT

The present invention will be explained in more detail by the followingexamples, which should not be construed as limiting the invention in anymanner.

EXAMPLE 1

o-Cresol novolak epoxy resin (softening point: 62° C. 5.3% by weight andepoxy equivalent: 200) Phenolic novolak resin (softening point: 90° C.and 2.7% by weight hydroxyl equivalent: 103) Spherical alumina 1(average particle diameter: 90.0% by weight  13.7 μm) Ultrafine silica 1(specific surface area: 180 m²/g) 0.5% by weight Silicone rubber(average particle diameter: 5 μm) 1.0% by weight Triphenylphosphine 0.1%by weight Carbon black 0.2% by weight Carnauba wax 0.2% by weight

The above components were mixed at room temperature by a mixer, and themixture was kneaded by twin roll at 70-120° C., cooled and then groundto obtain a resin composition. The resulting resin composition wasevaluated by the following methods.

[Evaluation Methods]

Spiral flow: This was measured using a mold for measurement of spiralflow which is in accordance with EMMI-1-66 at a mold temperature of 175°C., under an injection pressure of 6.9 MPa for a curing time of 2minutes. The unit of the spiral flow was cm. A spiral flow of 100 cm ormore was judged to be good.

Thermal conductivity: A molded product of 40 mm in diameter and 30 mm inthickness was prepared using a transfer molding machine at a moldtemperature of 175° C., under an injection pressure of 6.9 MPa for acuring time of 2 minutes. This was post-cured at 175° C. for 8 hours,and the thermal conductivity of the resulting molded article wasmeasured by a thermal conductivity meter (QTM-500 manufactured by KyotoElectronic Industry Co., Ltd.). The unit of the thermal conductivity wasW/mK. A thermal conductivity of 3 W/mK or more was judged to be good.

Warpage of package: A 225 pBGA (substrate: bismaleimide triazine/glasscloth substrate of 0.36 mm in thickness; package size: 24×24 mm with athickness of 1.17 mm; silicon chip: 9×9 mm in size with a thickness of0.35 mm) was prepared using a transfer molding machine at a moldtemperature of 175° C., under an injection pressure of 6.9 MPa for acuring time of 90 seconds, and this was post-cured at 175° C. for 8hours. The cured product was cooled to room temperature, and thereafterdisplacement in height direction was measured in diagonal direction fromthe gate of the package using a surface roughness meter, and a value inwhich the difference in displacement was largest was taken as thewarpage. The unit of the warpage was μm. A warpage of 100 μm or less wasjudged to be good.

Length of flash: In the same manner as in the measurement of warpage ofpackage, a 225 pBGA was molded, and the length of resin flash whichescaped from the venting portion of about 30 μm thick was measured. Theunit of the length of flash was mm. A length of flash of 1 mm or lesswas judged to be good.

Temperature cycle property: In the same manner as in the measurement ofwarpage of package, a 225 pBGA was molded, and this was post-cured at175° C. for 2 hours to obtain 10 samples, each. Each 10 samples weresubjected to temperature cycle test of 1000 cycles, one cycle of whichconsists of 65° C., 30 minutes and 150° C., 30 minutes. It was examinedwhether internal cracking and various separations at interface occurredor not. When the number of rejected packages in which cracking andseparation were observed was n, this is shown by n/10.

EXAMPLES 2-9 AND COMPARATIVE EXAMPLES 1-6 In accordance with theformulations as shown

in Table 1 and Table 2, resin compositions were prepared and evaluatedin the same manner as in Example 1. The results of the evaluation areshown in Table 1 and Table 2. Starting materials other than those usedin Example 1 are shown below.

-   -   Spherical alumina 2 (average particle diameter: 28.1 μm)    -   Ultrafine silica 2 (specific surface area: 240 m²/g)    -   Ultrafine silica 3 (specific surface area: 100 m²/g)    -   Ultrafine silica 4 (specific surface area: 340 m²/g)    -   Spherical silica (average particle diameter: 14.6 μm)

Polyorganosiloxane represented by the following formula (1):

TABLE 1 Example 1 2 3 4 5 6 7 8 9 O-Cresol novolak epoxy resin 5.3 5.34.0 5.3 5.0 7.3 5.3 5.5 5.2 Phenolic novolak resin 2.7 2.7 2.0 2.7 2.53.7 2.7 2.7 2.6 Spherical alumina 1 90.0 90.0 90.0 90.0 90.0 87.0 90.090.0 Spherical alumina 2 90.0 Ultrafine silica 1 (specific 0.5 0.5 0.50.5 0.5 0.5 0.3 0.7 surface area 180 m²/g) Ultrafine silica 2 (specific0.5 surface area 240 m²/g) Silicone rubber 1.0 1.0 Polyorganosiloxanerepresented 1.0 3.0 1.0 1.5 1.0 1.0 1.0 by the formula (1)Triphenylphosphine 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Carbon black 0.20.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Carnauba wax 0.2 0.2 0.2 0.2 0.2 0.2 0.20.2 0.2 Spiral flow (cm) 120 130 100 120 120 160 110 140 110 Thermalconductivity (W/Mk) 3.5 3.5 3.5 3.5 3.5 3.2 3.5 3.5 3.5 Warpage ofpackage (μm) 85 80 50 90 75 95 85 85 90 Length of flash (mm) <1 <1 <1 <1<1 <1 <1 <1 <1 Temperature cycle property: The 0/10 0/10 0/10 0/10 0/100/10 0/10 0/10 0/10 number of rejected packages after 500 cyclesTemperature cycle property: The 2/10 1/10 0/10 0/10 0/10 2/10 2/10 0/101/10 number of rejected packages after 1000 cycles

TABLE 2 Comparative Example 1 2 3 4 5 6 O-Cresol novolak epoxy resin 5.65.0 5.3 5.3 6.0 5.3 Phenolic novolak resin 2.8 2.5 2.7 2.7 3.0 2.7Spherical alumina 1 90.0 90.0 90.0 90.0 90.0 Spherical silica 90.0Ultrafine silica 1 (specific 0.1 1.0 0.5 0.5 surface area 180 m²/g)Ultrafine silica 3 (specific 0.5 surface area 100 m²/g) Ultrafine silica4 (specific 0.5 surface area 340 m²/g) Polyorganosiloxane 1.0 1.0 1.01.0 1.0 represented by the formula (1) Triphenylphosphine 0.1 0.1 0.10.1 0.1 0.1 Carbon black 0.2 0.2 0.2 0.2 0.2 0.2 Carnauba wax 0.2 0.20.2 0.2 0.2 0.2 Spiral flow (cm) 130 80 130 70 130 150 Thermalconductivity (W/Mk) 3.5 3.5 3.5 3.5 3.5 0.9 Warpage of package (μm) 8085 80 90 120 65 Length of flash (mm) 3 <1 2 <1 <1 <1 Temperature cycleproperty: 0/10 0/10 0/10 0/10 3/10 0/10 The number of rejected packagesafter 500 cycles Temperature cycle property: 0/10 1/10 1/10 0/10 10/100/10 The number of rejected packages after 1000 cycles

According to the present invention, an epoxy resin composition excellentin flash characteristics and thermal conductivity can be obtained, andarea mounting type semiconductor apparatuses produced using the resincomposition have little warpage and excellent temperature cycleproperties.

1-2. (canceled)
 3. A semiconductor apparatus in which a semiconductorelement is mounted on one side of a substrate and substantially only theone side of the substrate on which the semiconductor element is mountedis encapsulated with an epoxy resin composition, the epoxy resincomposition comprising, as essential components, (A) a sphericalalumina, (B) an ultrafine silica having a specific surface area of120-280 m²/g, (C) a silicone compound, (D) an epoxy resin, (E) aphenolic resin curing agent, and (F) a curing accelerator, the ultrafinesilica being contained in an amount of 0.2-0.8% by weight based on atotal weight of the resin composition.
 4. A semiconductor apparatus inwhich a semiconductor element is mounted on one side of a substrate andsubstantially only the one side of the substrate on which thesemiconductor element is mounted is encapsulated with the epoxy resincomposition, the epoxy resin composition comprising, as essentialcomponents, (A) a spherical alumina, (B) an ultrafine silica having aspecific surface area of 120-280 m²/g, (C) a silicone compound, (D) anepoxy resin, (E) a phenolic resin curing agent, and (F) a curingaccelerator, the ultrafine silica being contained in an amount of0.2-0.8% by weight based on a total weight of the resin composition,wherein the silicone compound (C) is a polyorganosiloxane and the amountof the silicone compound is 0.3-2.0% by weight based on the total weightof the resin composition.